In a wireless communication system, generally, a base station (BS) provides a service to a plurality of user equipments. The BS schedules user data with respect to the plurality of user equipments and transmits control information including scheduling information about user data along with user data. In general, a channel carrying the control information is called a control channel, and a channel carrying the user data is called a data channel. A user equipment (UE) monitors the control channel to find its control information and processes its data by using the control information. Here, monitoring refers to attempting to decode control channel candidates.
In order for the UE to receive user data allocated to the UE itself, it must necessarily receive control information about user data on the control channel. In this respect, however, generally, control information of a plurality of terminals are multiplexed in a single transmission interval in a given bandwidth. Namely, in order to provide a service to a plurality of UEs, the BS multiplexes the control information regarding the plurality of UEs and transmits them via a plurality of control channels. Then, each UE finds its own control channel among the plurality of control channels.
One of schemes for detecting particular control information from among the multiplexed control information is blind decoding. Blind decoding attempts to recover a control channel by using information of several combinations in a state that the UE does not have information required for recovering the control channel. Namely, the UE decodes all the control information provided to the UE until such time as it finds its control information in a state that the UE is not aware that the plurality of control information provided from the BS are its control information or where its control information is positioned. In order for the UE to discriminate whether or not certain information is its control information, the UE may use specific information of the UE. For example, when the BS multiplexes the control information of each UE, it may mask a specific identifier of each UE in a cyclic redundancy check (CRC) and transmit the same. The CRC is a code used for detecting an error. Upon receiving the control information, the UE damasks its specific identifier and checks the CRC to determine whether or not the received control information is its control information.
If the UE fails to properly detect its control information from among the multiplexed control information, it cannot decode user data on the data channel. Thus, it can be said that fast, accurate detection of the control information may significantly affect the performance of the overall system. However, it may have a difficulty in detecting the control information through the simple blind decoding.
Each UE may need different control information and use a channel encoding method using a different code rate, so the size of the control information of each UE may be different. Thus, the number of attempting to perform blind decoding within a control region in which the control information is transmitted may unexpectedly increase. As the detection attempt number of times increases, power consumption of a battery of the UE increases.
Thus, a method for effectively monitoring a control channel capable of reducing power consumption of the battery of the UE by reducing the detection attempt number to quickly detect control information is required.